This invention relates to a direct injection fuel injector for an internal combustion engine.
Combustion chamber deposits have been a cause of concern in gasoline internal combustion because such deposits are believed to affect, to name a few, driveability, emission, ignition plug fouling and degraded injector performance. In the case of a direct injection gasoline engine, deposits may be formed on the surfaces of the combustion chamber, valves, piston, injector and spark plugs. In particular, it is believed that these surfaces are often wetted with fuel, thereby increasing the likelihood of deposit formations. The formation of deposits on the surfaces of the injector is believed to cause flow capacity shift and spray pattern degradation that result in power loss, engine roughness and increased emissions for the direct injection gasoline engine. Moreover, it is believed that the direct injection fuel injector is especially affected since the injection pressure is oftentimes too low to mechanically dissociate the deposits that are formed on the wetted surfaces of the injector, such as the seat and needle or closure member.
Research on combustion deposits formations appears to indicate that the formation of deposits on the injector tip is dependent on a variety of factors including an injector tip temperature, injector protrusion into the combustion chamber, heat transfer from the injector to the coolant passages of the engine, types of fuel, surface geometry of the injector tip and coating or plating of the tip surfaces. The data also seems to indicate that where the injector tip temperature is above 110-140 degrees Celsius, a tendency for a formation of deposits is increased when the other factors are unchanged. Conversely, the data seems to indicate that below this temperature (approximately 120xc2x0 Celsius), the tendency for the formation of injector tip deposits is greatly reduced when the other factors are held constant.
The present invention provides for a method of optimizing a fuel injector tip position of a direct-injection fuel injector for use with a pre-selected engine. The fuel injector tip for use with the engine being located at a first axial position relative to a combustion chamber of the engine. In one embodiment, the method can be achieved by generating at least one map of an engine that indicates engine load, engine speed and injector tip temperature over the operating range of the engine operating at a generally stochiometric fuel mixture for a plurality of different fuel injectors; selecting at least one fuel injector from the plurality of fuel injectors where the injector tip temperature over the engine operating range does not exceed a set value; and verifying whether the selected fuel injector includes a tendency to form injector tip combustion deposits.
The present invention further provides for a method of optimizing a mounting position of a high-pressure direct injector in a combustion chamber of an engine. The injector has a central axis extending between an inlet and an injector tip. The injector tip being disposed at a first axial position with respect to a surface of the combustion chamber. In another embodiment, the method can be achieved, in part, by generating at least one map that relates engine load, engine speed and injector tip temperature for an operating range of the engine, the combination operating at a generally stochiometric air-fuel mixture; determining changes in fuel flow through the injector when the combination is operated at one or more selected points of the at least one map over a selected period of time; generating at least one tip characteristic map that relates changes in fuel flow at selected speed points of the at least one map for a plurality of different axial positions of the injector tip; generating at least one tip optimization map as a function of: (i) the plurality of axial positions of the fuel injector tip; (ii) changes in fuel flow; and (iii) a range of engine loads at the selected speed points from the at least one tip characteristic map; and selecting an axial position of the fuel injector tip having a least amount of change in fuel flow over the range of engine loads from the at least one tip optimization map.